Our goal is to use 3-D reconstruction as a quantitative method to establish the accumulated density of the dense granules of human platelets. On average, there are 4-6 dense granules (DG) per platelet. Some people have prolonged bleeding times of unknown etiology, and it has been found that they have less than the normal average number of DGs. However, it has also been demonstrated that another group of people with the identical presentation have a normal number of platelet DGs. Through quantitation of reconstructed platelets from both groups, we wish to determine if there are DG volume differences between these two groups. This year, most of the effort was devoted to optimizing sample preparation. The goal is to use selective staining techniques to optimize the visibility of the dense granules without over-staining the rest of the cell. Six different preparations were examined using 1.5lm sections photographed in strereo on the HVEM. We now believe that whole-mount preparations may be best for quantitative work. Nevertheless the data already collected is useful for depiction of 3d platelet morphology.